Why do you want to do this would be my number one consideration. Its not hard to do, I recently installed XP Pro on a older model laptop as a duel boot with windows 2000. I did this only due to some software that was ONLY compatible with XP. Another consideration for me was, does the hardware meet specs to run XP smoothly. Adding additional RAM done the trick.

Also, there is no need to ask the same question in two different posts. Ask once, sooner or later someone around here is bound to help you. Welcome to Techspot!!!

You may have to repair your 2003 installation. The reason halo71 didn't have to is because XP came after 2000. Microsoft has allowed newer OS to be installed in dual boot after an earlier OS is on, but it doesn't go as smoothly when you are putting an older OS on after a newer one.